This invention related to a positive type photosensitive anionic electrodeposition coating resin composition, an electrodeposition bath using the same, an electrodeposition process and a process for producing printed circuit boards.
As processes for forming resist patterns on surfaces of substrates, there has frequently been used a process comprising forming a photosensitive layer on a substrate surface, irradiating the photosensitive layer with actinic light, followed by development. As to formation of photosensitive layer, there have been known, for example, dip coating, roll coating, curtain coating, etc., using a photosensitive resin composition solution (a coating fluid), and a laminating process wherein a photosensitive film which is obtained by forming a photosensitive layer on a substrate film previously is laminated on a substrate surface using a laminator, etc. Among these processes, the laminating process using the photosensitive film are mainly employed particularly in the field of printed circuit board production due to formation of the photosensitive layer with a uniform thickness easily.
With recent progress of higher density and higher precision of printed circuit boards, resist patterns having higher quality are required now. That is, there are required resist patterns having no pin holes and good in adhesion to an underlying substrate surface. In order to meet such a requirement, the laminating process using the photosensitive film and now employed mainly is to be known having a limit. According to the laminating process, conformability to unevenness of substrate surface caused by scars at the time of substrate production, ununiformity of polishing, meshes of glass cloth present in an inner layer of substrate, ununiformity of pits and the like of copper plating on the surface, is poor, resulting in difficulty in obtaining sufficient adhesiveness. Such difficulty can be removed to some extent by carrying out the lamination of photosensitive film under reduced pressure (Japanese Patent Examined Publication No. 59-3740), but a special and expensive apparatus is necessary for such a purpose.
Under such circumstances, solution coating processes such as dip coating, roll coating, curtain coatings, etc. have been noticed again recently. But these processes have problems in that control of film thickness is difficult, uniformity of film thickness is insufficient, pin holes are generated, and the like.
Recently, there is proposed a new process for forming a photosensitive film by electrodeposition (Japanese Patent Unexamined Publication No. 62-235496). According to this process, there are advantages in that (1) adhesiveness of a resist to a substrate is improved, (2) conformability to unevenness of substrate surface is good, (3) a photosensitive film with a uniform film thickness can be formed in a short time, (4) since the coating fluid is an aqueous solution, pollution of working circumstances can be prevented, and there is no problem in prevention of disasters. Thus, there are made some proposals as to positive type photosensitive electrodeposition which seems to be effective for producing printed circuit boards having through-holes. In most cases, a quinonediazido group as a photosensitive group is used, but there are problems in that photosensitivity is low and water disposition stability of photosensitive materials is poor.
On the other hand, as a pattern forming process for producing electronic parts such as semiconductor elements, magnetic bubble memories, integrated circuits, etc., there are proposed processes using many chemical amplified system positive type photosensitive materials comprising a compound which can generate an acid upon irradiation with actinic light, and a compound which is decomposed by the acid generated and shows a property of enhancing solubility in a developing solution. These processes can be expected to show extremely higher sensitivity than the process of using the quinonediazido group. But such materials have not practically been used for electrodeposition. This is because known chemical amplified positive type photosensitive materials are dissolved in organic solvents and used for forming photosensitive films by a coating method, so that these materials cannot be dispersed in water as they are and thus cannot be used as an electrodeposition coating resin composition. In order to use these materials for electrodeposition, it is necessary to fundamentally reconstitute chemical amplified positive type photosensitive materials.